The present invention disclosed herein relates to an electronic device, and more particularly, to a photo detector driving an avalanche photodiode in the Geiger mode.
Until recently, a variety of photo detection devices have been developed. Especially, a semiconductor photo detection device may be classified into a PN and PIN photo detector and an avalanche photo detector based on whether there is a gain or not. The PN and PIN photo detector detects light through a photoelectric current flowing in proportion to an intensity of the detected light. Moreover, the avalanche photo detector provides a gain through an avalanche process in order to increase the sensitivity about detected light.
However, there are limitations in obtaining a gain through the avalanche process. To resolve the above limitations, the avalanche photodiode is driven in the Geiger mode. That is, if a higher reverse bias than a breakdown voltage is applied to an avalanche photodiode (APD), a higher gain may be realized. Driving of the APD under this bias condition is the so-called Geiger mode. In the Geiger mode, it is possible to theoretically detect single photon.
In general, the APD provides a relatively low gain in a lower reverse bias state than a breakdown voltage VBR. Instead of that, during the lower reverse bias state than a breakdown voltage, the APD provides a linear characteristic generating a photoelectric current in proportion to incident photon quantities. However, the APD in the Geiger mode does not generate a photoelectric current proportional to photon quantities any more. Instead of that, the APD provides a much greater gain than a gain of a linear characteristic region in the Geiger mode. Accordingly, a photo detection of a low light quantity is possible in the Geiger mode. Furthermore, since the Geiger mode provides a relatively greater photoelectric current than a linear mode, photo detection is possible without an additional complex low-noise amplifier.
Recently, many attempts for practical applications of the APD have been made. Especially, researches using the APD as a photo sensor to realize a three-dimensional image are being in progress. For example, if a photo detector using the APD is configured in an array, on detecting lights reflected after a single laser pulse is projected, information about an entire three-dimensional structure of an object may be obtained. This device is called a light detection ranging (LIDAR) system.
The number of photons returning to a detector array after being scattered from an object is reduced as their travelling distance is longer. As a result, its detected signal is weak. Thus, a photo detector array may operate in the Geiger mode in order to detect the weak signal. Moreover, technologies for configuring the photo detector array with an integrated circuit to form a two-dimensional focal plane and maximizing photo detection efficiency are required.